1. Field of the Invention
This invention relates to a digital modulating device for modulating a digital signal, and to a recording apparatus for recording a digital signal on a recording medium. More particularly, the invention relates to a digital modulating device for converting n-bit data into m (&gt;n)-bit data, and to a digital recording apparatus for recording a signal component having a specific frequency as a pilot signal added to main information while controlling the intensity of the signal component.
2. Description of the Related Art
In conventional apparatuses for recording a digital signal on a recording medium, there has been known a technique in which high-density recording is performed by recording the signal by forming a large number of tracks on the recording medium. When reproducing a recorded signal from such an apparatus, a so-called tracking control operation must be performed so that a reproducing head can assuredly trace high-density recording tracks and digital information can be reproduced in an excellent state.
In an ordinary tracking operation, a pilot signal for tracking control is superposed on a recording signal during a recording operation, and a tracking error is detected using the pilot signal. A technique of superposing a pilot signal having a low frequency which is not influenced by an azimuth and the like is generally adopted.
FIG. 1 is a diagram illustrating a conventional recording pattern of pilot signals, in which two kinds of pilot signals f1 and f2 are periodically multiplexed with an information signal on a large number of tracks recorded in parallel on a recording tape T. In FIG. 1, symbol F.sub.0 represents a track on which a pilot signal is not multiplexed, symbol F.sub.1 represents a track on which the pilot signal f1 is multiplexed, and symbol F2 represents a track on which the pilot signal f2 is multiplexed.
In a reproducing operation, while a head traces a track F.sub.0, the crosstalk component of the pilot signal f1 from a track F.sub.1 adjacent to the track F.sub.0 and the crosstalk component of the pilot signal f2 from a track F.sub.2 adjacent to the track F.sub.0 are compared with each other to form a tracking-error signal.
However, when it is intended to apply the above-described tracking control (of multiplexing pilot signals) to a digital recording apparatus, a pilot signal and a recording signal (containing main information) are superposed independently. As a result, the S/N ratio of a digital signal in a reproducing operation is degraded, causing an increase in the error rate of reproduced data. This causes degradation in a reproduced image when the tracking control is applied to a digital VCR (video cassette recorder).
Furthermore, a strong spectrum of the digital recording signal is present in the vicinity of the frequency of the pilot signal, thereby causing degradation in the S/N ratio of the pilot signal in a reproducing operation, as well as degradation in tracking accuracy. This also causes degradation in a reproduced image when the tracking control is applied to a digital VCR.
Recently, there has been proposed a technique in which a pilot signal is superposed on a digital recording signal while including a pilot-signal component in a digital modulating signal. However, a very complicated circuit configuration is required for realizing such a proposal.